1. Field of the Invention
This invention relates to a power plant mounting bush which can be revolve automatically according to engine vibration conditions to show different damping characteristics.
2. Description of the Prior Art
An automobile the engine produces power by movement of pistons, connecting rods and a crank shaft. Weight center of engine continues to be changed periodically by vertical movement of pistons and connecting rods owing to structural reason of an engine. Since inertial force according to piston's reciprocal movement, inertial force according to connecting rods' movement lateral to the crankshaft and rotational force applied to the crankshaft are periodically changed, there are generated vertical and horizontal vibrations in the engine.
Such vibrations are rather severe in an engine having fewer cylinders, and the vibrations have relatively high amplitude at a low speed of the engine but relatively low amplitude at a high speed of the engine according to the engine speed. An engine is normally supported by a chassis or a body of a vehicle together with a transmission and/or a clutch, on which the engine or a power plant (general term indicating assembly of engine, transmission and/or clutch) is mounted by elastic mounting means therebetween for absorbing such vibrations in order to prevent vibrations of the engine from being transmitted to the chassis or body not to hinder passenger comfort. Such mounting means is generally called as engine mount, power plant mount, etc.
Types of engine mounts or power plant mounts are divided into a rubber mount with a rubber insulator and a hydraulic mount including hydraulic fluid within a rubber insulator according to their materials or structure, and are also divided into a flat-type mount for supporting a lower surface of the engine or the power plant and a bush-type mount for supporting torque roll shaft according to their utility.
The most important factor considered in design of the engine mount or the power plant mount is the damping characteristics of an insulator. Generally the engine mount requires a high damping value against high amplitude vibrations for rapidly absorbing engine shocks and also needs to have a low damping value but a high spring constant against the low amplitude vibrations in order to reduce the indoor noise of a vehicle.
FIG. 1 shows a conventional rubber typed power plant mounting bush.
As shown, the conventional power plant mounting bush 1 includes an inner pipe 2 centrally mounted thereon and a rubber insulator 4 formed therearound and having two holes 3 at the upper and lower parts thereof. The rubber insulator 4 has a changing rubber-space rate toward its diagonal directions according to its shape, so as to provide a different damping value and a different spring constant toward its radial directions, respectively. However, the rubber type power plant mount 1 is installed conventionally and fixedly considering vibrational average forces applied thereto to show constant damping and elastic characteristics regardless of amplitude or frequency of applied vibrational force F toward respective radial directions.
However, a power plant mounting bush having such constant characteristics could not meet requirements of ever-progressing low indoor noise and high comforts, because vehicle vibrations are vary in amplitude and frequency in accordance with engine speed even in the same direction.
Accordingly, it is an object of the present invention to provide a power plant mounting bush whose insulator damping characteristics can be changed according to vehicle speed.